1. Field of the Invention
This invention relates to an air-core coil for sensing the current in a circuit breaker and, more specifically, to a unitary body mounting bracket for the air-core coil.
2. Background Information
A common type of power air circuit breaker has a molded casing housing and multiple pole assemblies all driven by a common operating, or trip, mechanism. Contact arm carriers support movable contacts which engage stationary contacts when the contact arm carrier is in the closed position. The movable contact is in electrical communication with a load conductor which extends through the housing. Additionally, the load conductor is attached by a fastener to the housing. The stationary contact is in communication with a line conductor which extends through the housing. The line conductor is structured to be coupled to an electrical source. The load conductor is structured to be coupled to an end use that relies on electricity.
Traditionally, power air circuit breakers using an electronic trip device have included both a primary current sensor and a secondary current sensor. The primary current sensor may be a toroidal current sensor disposed about the load conductor. The optional secondary current sensor is an air-core coil. Both the primary and secondary sensors are coupled to an electronic trip unit that is structured to detect an over-current condition and, when an over-current occurs, actuate the trip mechanism in the circuit breaker.
As shown in FIG. 1, a prior art air-core sensor assembly includes an air core coil 1 and a mounting bracket 3. The air-core coil mounting bracket 3 included a metal portion 4 and an insulated portion 5. The metal portion 4 was an elongated body that attached to the load conductor fastener 6. Although the load conductor fastener 6 is not disposed within the perimeter of the toroidal current sensor 7, the metal portion 4 of the bracket extended along the load conductor 2 so that the air-core coil was disposed within the perimeter of the toroidal current sensor 7. That is, the air-core coil 1 was disposed adjacent to the fastener 6 head, not above the fastener 6 head. This configuration required the toroidal current sensor 7 to have an inner radius large enough to accommodate the air-core coil 1.
There is a trend toward smaller circuit breakers. With a smaller circuit breaker, the radius of the toroidal current sensor must be reduced, thereby eliminating the space in which the air-core sensor assembly is disposed. Thus, the former, two-part mounting bracket cannot be used with newer circuit breakers. Additionally, the two-piece mounting bracket required assembly which added an additional manufacturing step and cost.
There is, therefore, a need for an air-core sensor assembly mounting bracket that is made from one piece.
There is a further need for an air-core sensor assembly mounting bracket that is not structured to mount the air-core sensor within the perimeter of the toroidal current sensor.
There is a further need for an air-core sensor assembly mounting that is compatible with existing circuit breaker hardware.
These needs, and others, are met by the present invention which provides a unitary body, i.e., one-piece, mounting bracket having a U-shaped body and at least one retaining form. The retaining form is structured to be coupled to a fastener on the load conductor. The retaining form is located below the U-shaped body. That is, the U-shaped body has a longitudinal axis and the retaining form is located substantially below the longitudinal axis.
Thus, when the mounting bracket is attached to a fastener coupling the load conductor to the circuit breaker housing, and an air-core coil is disposed within the U-shaped body, the air-core coil will be disposed, generally, above the fastener heads. Because the fastener heads are not within the perimeter of the toroidal current sensor, the air-core coil will be located outside of the toroidal current sensor perimeter. Accordingly, because the air-core coil is not disposed within the perimeter of the toroidal current sensor, the toroidal current sensor can have an inner radius and, therefore the outer radius as well, that is closer to the load conductor than prior art toroidal current sensors. Because the volume occupied by the toroidal current sensor is smaller, the circuit breaker may be made smaller too.
An added advantage of the unitary body mounting bracket is that, it is less expensive to manufacture and is easier to install than the prior art two-piece mounting bracket.